refrigeration installation for cooling at least one piece of furniture and/or a walk-in cooler, and for heating at least one room of premises, and an air heat exchanger for such an installation

ABSTRACT

The air exchanger comprises at least one tubular circuit for evaporating a refrigerant and thermally conducting fins ( 40 ) fastened to the tubular evaporation circuit and at least one tubular circuit ( 35 ) for condensing a refrigerant, which is connected via thermally conducting fins ( 40 ) to the evaporation circuit.

The present invention relates to the technical field of refrigerationinstallations that are used for cooling various substances, and inparticular foodstuffs.

In the above-mentioned field, it is known, in particular insupermarkets, to implement a refrigeration installation comprisinghigh-pressure and low-pressure refrigerant fluid circuits connected toone or more refrigeration units such as a reach-in coolers orrefrigerated display cabinets, or indeed walk-in coolers. Therefrigeration installation further comprises a compression unit thatsucks in refrigerant fluid from the low-pressure circuit and delivers itonce compressed into the high-pressure circuit. Downstream from thecompression unit, the installation further comprises an exteriorcondenser at which the refrigerant fluid is cooled before beingre-directed towards the refrigeration unit or towards an intermediatestorage tank. Such an installation is fully satisfactory as regardskeeping fragile substances or foodstuffs at low temperature settings.However, the heat extracted from the refrigeration units and resultingfrom the work of the compression unit is dissipated to the outside,constituting a total loss of energy that, in view of energy costs and ofsustainable development requirements, is unsatisfactory.

In order to remedy that drawback of wasting energy, Patent ApplicationEP 0 431 797 proposes to adapt, in a unit heater, a condenser circuitfed with a gaseous high-pressure refrigerant fluid in such manner as torecover heat for the purpose of heating premises. Unfortunately, theinstallation proposed by Application EP 0 431 797 does not make itpossible to have enough heat to achieve, on its own, satisfactoryheating in the winter.

Patent Application EP 1 921 401 proposes a refrigeration installationfrom which the extracted heat is recovered for the purpose of heating aheat accumulator that is in communication with a central-heating watercircuit and/or with a hot-water circuit. The installation disclosed inPatent Application EP 1 921 401 further comprises an exterior evaporatorthat, during the winter period, makes it possible to take from theoutside the extra heat necessary for satisfying heating needs. Duringthe summer period, the heat extracted by the installation disclosed inEP 1 921 401 is removed mainly to an exterior condenser that is totallyindependent of the exterior evaporator. Although that installation makesit possible to procure extra heat under satisfactory conditions byoperating as a heat pump, it suffers from the drawback of not offeringsufficient power to cover the heating needs for heating premises, sothat additional electric heater means are provided that are detrimentalto the environmental performance of the installation. In addition, thatinstallation makes provision for the evaporator to be defrosted by cyclereversal that also affects the performance of the installation insofaras the design of the exterior evaporator must then result from acompromise between its operating modes as an evaporator and as acondenser. Finally, Patent Application EP 1 921 401 makes provision toplace the interior heat exchanger for the heating in series with theexterior condenser, and upstream therefrom, thereby detrimentallyaffecting the energy efficiency of the installation and requiring alarge quantity of refrigerant fluid in the liquid state to fill thecircuit downstream from the heat exchanger when the refrigerant fluid isfully condensed therein.

Thus, the need has arisen for a novel type of refrigeration installationthat makes it possible firstly to recover at least a fraction of theheat available from the refrigerant fluid for the purpose of heatingpremises, and secondly, possibly, to supplement this additional heatunder economically and ecologically satisfactory conditions, and thatalso, for equivalent absorbed electrical power, has performance higherthan the performance of known refrigeration installations and lowermaintenance costs.

In order to achieve this object, the invention provides a refrigerationinstallation having refrigerant fluid and comprising at least:

high-pressure and low-pressure circuits;

a refrigeration unit comprising at least one evaporator disposed in apiece of furniture or in a walk-in cooler, and connected to thehigh-pressure and low-pressure circuits;

an air-conditioning unit comprising at least one heat exchanger that isdisposed inside a room of premises, and that further comprises at leastone condenser connected to the high-pressure and low-pressure circuits;

an exterior unit comprising at least one air heat exchanger that isdisposed outside and that comprises a condensation tube circuitconnected to the high-pressure and low-pressure circuits;

a main compression unit connected to the high-pressure and low-pressurecircuits;

an auxiliary compression unit connected to the high-pressure andlow-pressure circuits; and

a control unit that controls at least operation of the refrigerationinstallation.

According to the invention, the refrigeration installation ischaracterized in that:

the air heat exchanger of the exterior unit further comprises:

an evaporation tube circuit adapted to be fed with low-pressurerefrigerant fluid only and connected to the high-pressure andlow-pressure circuits; and

thermally conductive fins interconnecting the evaporation tube circuitand the condensation tube circuit by being secured to the evaporationand condensation tube circuits;

the condensation tube circuit being adapted to be fed with high-pressurerefrigerant fluid only and being dimensioned so as to dissipate all ofthe heat resulting from keeping each refrigeration unit at temperaturesettings when a summer temperature prevails outside;

the control unit is adapted to place the installation:

either in a purely refrigeration operating mode, in which the power ofall of the compression units is available for extracting heat from eachrefrigeration unit only;

or in a combined refrigeration and heat pump operating mode, in whichthe power of the auxiliary compression unit is available for extractingheat from the exterior unit, and the power of each other compressionunit is available for extracting heat from each refrigeration unit;

the compression units are dimensioned so that their cumulative power issufficient for maintaining each refrigeration unit at temperaturesettings when a summer temperature prevails outside and when theinstallation is in purely refrigeration mode.

Such a refrigeration installation of the invention is particularlysuitable for cooling refrigeration units and for heating a room or someother portion of premises with the heat recovered from the refrigerationunits and resulting from the compression of the refrigerant fluid. Tothis end, implementing an auxiliary compression unit makes it possible,when the heat recovered from the refrigeration units is not sufficientto heat the room satisfactorily, to take from the outside the heat thatis lacking and that is necessary to reach the satisfactory heatinglevel.

In accordance with the invention, the heat exchanger of eachair-conditioning unit may be of any suitable type. Thus, the heatexchanger of each air-conditioning unit or of each of some units only,may be a heat exchanger making it possible to heat a heat transferliquid, such as, for example, but not exclusively, the water of aheating circuit, or indeed the water of a hot-water system. The heatexchanger of each air-conditioning unit, or of each of some units only,may also be an air heat exchanger or “unit heater”. Implementing such anair heat exchanger offers the advantage of heating the air directlywithout using an intermediate heat transfer fluid, and makes it possibleto procure optimum efficiency and to simplify implementation and use ofthe refrigeration installation of the invention. Naturally, theinstallation of the invention is also suitable for implementing aplurality of air-conditioning units having different types of heatexchanger.

In addition, implementing an exterior unit designed for making itpossible both to remove all of the heat in the summer, and also torecover additional heat in the winter with circuits interconnected byfins makes it possible to obtain a dual-purpose exterior unit that iscompact.

Various embodiments of the installation may be considered. Thus, thehigh-pressure and low-pressure circuits may comprise a mainhigh-pressure circuit, a secondary high-pressure circuit, and a mainlow-pressure circuit. The evaporator of the air-conditioning unit isthen fed with refrigerant fluid by the main high-pressure circuit via anexpansion valve and is connected to the main low-pressure circuit. Theevaporation circuit of the exterior unit is fed by the mainhigh-pressure circuit via an expansion valve and is connected to anauxiliary low-pressure circuit, while the condensation circuit of theexterior unit is connected to the main high-pressure circuit upstreamfrom the evaporators. The main compression unit sucks in refrigerantfluid from the main low-pressure circuit and delivers compressedrefrigerant fluid to the main high-pressure circuit, while the auxiliarycompression unit sucks in refrigerant fluid from the auxiliarycompression unit and delivers compressed refrigerant fluid to the mainhigh-pressure circuit.

The installation may further comprise an isolation valve that iscontrolled to open or close the communication between the auxiliarylow-pressure circuit and the evaporation circuit of the exterior heatexchanger, and a bypass circuit that connects the main low-pressurecircuit to the secondary low-pressure circuit and that is equipped witha bypass valve controlled to open or close the bypass circuit. Thecontrol unit is then adapted:

in the purely refrigeration mode, to close the isolation valve and toopen the bypass valve, so that the power of the auxiliary compressionunit is available for extracting heat from each refrigeration unit only;

in the combined refrigeration and heat pump operating mode, to open theisolation valve and to close the bypass valve, so that the power of theauxiliary compression unit is available for extracting heat from theexterior unit.

In a variant of the invention, the control unit is adapted to go fromthe combined operating mode to the purely refrigeration operating modeand vice versa as a function of the refrigeration needs.

It should be noted that the large surface area of the condensationcircuit, resulting from it being dimensioned to remove heat in thesummer, makes it possible to procure very high effectiveness fordefrosting the exterior unit while it is operating in combined mode. Tothis end, in a variant embodiment of the invention, the installationfurther comprises defrosting means for defrosting the heat exchanger ofthe exterior unit, which means are adapted so that, when theinstallation is operating in combined mode, they temporarily feed thecondensation circuit of the exterior unit. Implementing such defrostingmeans makes it possible to preserve the effectiveness of the exteriorheat exchanger in particular when said heat exchanger is used as a heatsource during the winter period. The use of the condensation circuit,designed to withstand the high pressures of the refrigerant fluid, makesit possible to avoid using defrosting by cycle reversal at theevaporation circuit, thereby offering the advantage firstly of not beingobliged to dimension the evaporation circuit for high pressures, andsecondly of avoiding subjecting the evaporation circuit to the thermalshock resulting from rapidly going from a negative temperature to apositive temperature, e.g. greater than 30° C. and, furthermore, ofavoiding the risks of sucking in liquid on re-starting in heat pumpmode. In addition, the fins interconnecting the condensation circuit andthe evaporation circuit damp the expansion differences between thecondensation circuit and the evaporation circuit during defrostingstages, thereby reducing the mechanical stresses to which these circuitsare subjected. By separating the evaporation circuit from thecondensation circuit in the exterior unit, the invention makes itpossible to optimize their dimensioning for their nominal ratedoperating conditions with acceptable head loss, and fluid speeds thatare under control, making it possible for good oil return to beachieved, thereby contributing to the performance of the refrigerationinstallation as a whole.

According to a characteristic of the invention, the installation furthercomprises:

frost assessment means for assessing the frost on the exterior heatexchanger; and

at least one controlled valve for feeding the condensation circuit ofthe air heat exchanger;

and the control unit is adapted to cause a feed valve for feeding thecondensation circuit to open whenever the frost on the heat exchangerexceeds a certain threshold.

In accordance with the invention, frost detection may be performed invarious manners such as, for example, by monitoring the load on aforced-flow fan motor of the heat exchanger so as to deduce from anyincrease in load on the motor that frost has appeared on the heatexchanger. In another embodiment, the frost assessment means comprisemeans for measuring the humidity in the air entering and exiting fromthe heat exchanger.

In accordance with a characteristic of the invention, the control unitis adapted to reverse the direction of operation of an extractor fanequipping the exterior heat exchanger at the end of defrosting thereof.This rotation reversal makes it possible to obtain optimum drying of theheat exchanger of the exterior unit.

In an embodiment, the installation may be adapted to activitiesrequiring a plurality of low temperature levels, such as, for example,activities in which it is necessary to keep some substances cool atpositive temperatures and also to keep some substances frozen atnegative temperatures. The refrigeration installation of the inventionthen further comprises:

a secondary low-pressure circuit for refrigerant fluid;

a secondary refrigeration unit comprising at least one evaporator thatis disposed in a piece of furniture or in a walk-in cooler, that is fedwith refrigerant fluid by the main high-pressure circuit via anexpansion valve, and that is connected to the secondary low-pressurecircuit; and

a secondary compression unit that sucks in refrigerant fluid from thesecondary low-pressure circuit and that delivers compressed refrigerantfluid into the main high-pressure circuit;

the control unit being adapted to cause the secondary compression unitto operate.

Implementing the secondary compression unit delivering compressedrefrigerant fluid to the same main high-pressure circuit as the othercompression units makes it possible to use all of the heat energyrecovered by all of the compression units for the purposes of heatingthe room(s) in which the unit heaters are situated.

In accordance with a characteristic of the invention, the auxiliarycompression unit power is not sufficient to cool the room under summeroutside temperature conditions.

In an embodiment of the invention, at least one unit heater of theair-conditioning unit is adapted to be reversible and to operate as acondenser or as an evaporator, and the installation further comprisesmeans for feeding refrigerant fluid to each unit heater operating as anevaporator.

In a variant of this embodiment, the auxiliary compression unit hassufficient power to cool the room with summer outside temperatures.

The invention also provides an air heat exchanger for a refrigerationinstallation of the invention, which air heat exchanger comprises:

a condensation tube circuit adapted to be fed with high-pressurerefrigerant fluid only;

an evaporation tube circuit adapted to be fed with low-pressurerefrigerant fluid only; and

thermally conductive fins interconnecting the evaporation tube circuitand the condensation tube circuit by being secured to the evaporationand condensation tube circuits.

According to the invention, the condensation circuit has heat exchangepower that is sufficient to remove heat in the summer period, i.e. theabsolute value of the thermal power of the condensation tube circuit isgreater than or equal to the absolute value of the thermal power of theevaporation tube circuit.

The heat exchanger of the invention offers the advantage of having anevaporation circuit that is distinct from the condensation circuit sothat each of these circuits is appropriately dimensioned for optimallyperforming its condensing function or its evaporating function, unlike aheat exchanger in which the circuit is adapted for combined operationeither as a condenser or as an evaporator. The design of the heatexchanger of the invention thus enables it to procure optimum energyefficiency. In addition, implementing fins that are common to theevaporation circuit and to the condensation circuit makes it possible tooptimize the heat exchanges during defrosting that can then be shorterthan the defrosting time in a design consisting merely in juxtaposing acondenser and an evaporator one above the other. In addition, as statedabove, the fins mechanically damp differential expansion phenomenaduring defrosting.

According to a characteristic of the invention, the thermal power of thecondensation tube circuit has a value lying in the range 1 times theabsolute value of the thermal power of the evaporation tube circuit to 5times said absolute value.

According to another characteristic of the invention, the heat exchangesurface area of the condensation tube circuit represents in the range50% of the sum of the heat exchange surface areas of the condensationand evaporation tube circuits to 80% of said sum.

In an embodiment of the air heat exchanger, under normal conditions ofuse, the condensation circuit is situated at least in part below theevaporation circuit. This configuration makes it possible to makeadvantageous use of convection phenomena so as to accelerate defrostingof the evaporation circuit. In another embodiment of the heat exchanger,the condensation circuit and the evaporation circuit comprise loops ortube sheets and certain loops or sheets of the evaporation circuit aresuperposed on and interleaved between the loops or sheets of thecondensation circuit.

In an embodiment of the heat exchanger, the fins extend substantiallyvertically.

In a variant of the invention, the evaporation and condensation circuitshave rectilinear main tubes that are inclined by a few degrees relativeto the horizontal, thereby facilitating run-off of water.

In another variant of the invention, the condensation circuit comprisesat least one tube sheet that forms the first tube sheet starting fromthe bottom of the heat exchanger. This first tube sheet advantageouslyforms a surface on which a fraction of the water present in the aircondenses or is deposited, thereby reducing the load of the air flowingin the heat exchanger, and thus reducing the speed at which frostappears on the evaporation circuit.

In accordance with a characteristic of the invention, the heat exchangerfurther comprises at least one electric fan for forcing air to flowthrough the heat exchanger.

Naturally the various characteristics, variants, forms and embodimentsof the installation and/or of the heat exchanger may be associated withone another in various combinations insofar as they are not mutuallyincompatible or mutually exclusive.

Furthermore, various other characteristics and advantages of theinvention appear from the description given with reference to theaccompanying drawings that show non-limiting embodiments of an air heatexchanger and of refrigeration installations of the invention, and inwhich:

FIG. 1 is a diagrammatic view of a refrigeration installation of theinvention;

FIG. 2 is a longitudinal section view a heat exchanger of the inventionthat is suitable for being implemented in the installation shown in FIG.1;

FIG. 3 is a cross-section view of the heat exchanger on line III-III ofFIG. 2; and

FIG. 4 is a diagrammatic view of another embodiment of a refrigerationinstallation of the invention.

A refrigeration installation of the invention, as shown in FIG. 1 anddesignated overall by reference 1, includes a main high-pressurerefrigerant fluid circuit 2 on which a high-pressure tank 3 is disposedfrom which a branch 2 _(a) extends for feeding at least one andgenerally more main refrigeration units R_(P) with high-pressurerefrigerant fluid. Such a refrigeration unit R_(P) includes at least oneevaporator disposed in a piece of furniture or in a walk-in cooler. Theevaporator is then fed with refrigerant fluid in the liquid state by themain high-pressure circuit 2 _(a) via an expansion valve. The evaporatoris also connected to a main low-pressure circuit 4. The refrigerationinstallation 1 also includes at least one and, in the example shown,three air-conditioning units 5 disposed inside one or more rooms ofpremises. In the example shown, each air-conditioning unit comprises atleast one air heat exchanger or unit heater equipped with at least onecondenser 6 that is connected to the main high-pressure circuit 2upstream from the evaporators of the refrigeration units R_(P) and, inthe example shown, also upstream from the tank 3 of high-pressurerefrigerant fluid. The installation 1 also includes a main compressionunit 10 that sucks in the refrigerant fluid from the main low-pressurecircuit 4 so as to deliver it as compressed into the main high-pressurecircuit 2 upstream from the condensers 6, from the high-pressure tank 3,and, naturally, from the evaporators that it feeds. The main compressionunit 10 comprises at least one and, in the example shown, threecompressors 11 connected in parallel to the high-pressure circuit 2 andto the low-pressure circuit 4. Operation of the compression unit 10 isthen controlled by a control unit 12.

The refrigeration installation as defined above operates in thefollowing manner.

Since each main refrigeration unit R_(P) is provided with an independentregulator device, it causes a valve to open for feeding its evaporatorwith high-pressure refrigerant fluid via an expansion valve as and whennecessary to maintain a setpoint temperature in it. Operation of therefrigeration unit induces an increase in pressure in the mainlow-pressure circuit 4 that the control unit 12 detects in order totrigger operation of the main compression unit 10 that then sucks inlow-pressure refrigerant fluid in a low-pressure gas state so as todeliver it in the high-pressure gas state to the main high-pressurecircuit 2. On exiting from the main compression unit 10, the refrigerantfluid finds itself in the main high-pressure circuit 2 in the gas stateand at a high temperature of the order of in the range 60° C. to 80° C.The invention then proposes to use the heat from the high-pressurerefrigerant fluid in the gas state to heat one or more rooms of premisesvia the unit heaters 5 that have their condensers 6 fed via the valves13 controlled by the control unit 12. Thus, all of the heat recovered atthe refrigeration units is used for heating the rooms of the premises.On exiting from the condensers, the refrigerant fluid is in thehigh-pressure liquid state. In order to facilitate understanding, thoseportions of the main high-pressure circuit in which the high-pressurerefrigerant fluid is in the gas state are referenced 2, while thoseportions in which the refrigerant fluid is mainly in the liquid stateare referenced 2 _(a).

The heat recovered at the refrigeration units can, in some situations,in particular in the winter period, be insufficient for heating thepremises to an acceptable or indeed comfortable setpoint temperature.The term “the winter period” is used to mean a period in which theaverage outside temperature is less than 18° C. The invention thenproposes to take the heat or the calories that are lacking from theoutside. To this end, an exterior unit 15 is implemented that comprisesat least one heat exchanger 17 that comprises an evaporation circuit 18connected to the main high-pressure circuit 2 via an expansion valve 19.The evaporation circuit 18 is also connected to an auxiliarylow-pressure circuit 20 that feeds an auxiliary compression unit 21. Theauxiliary compression unit 21 comprises at least one and, in the exampleshown, two compressors 22 that are connected in parallel to theauxiliary low-pressure circuit 20 and to the main high-pressure circuit2. The auxiliary compression unit 20 then sucks in via the auxiliarylow-pressure circuit 20 the refrigerant fluid in the gas state comingfrom the evaporator 18 of the heat exchanger 17 so as to compress it andto deliver it into the main circuit 2. The auxiliary compression unit 20is then controlled by the control unit 12 that modulates operation ofone of or both of the compressors 22 depending on needs. Thus, theauxiliary compression unit 21 and the exterior heat exchanger 5 operateas a heat pump and take from the outside air the extra heat necessaryfor maintaining the setpoint temperature in the premises by means of theair-conditioning units 5. Thus, the refrigeration installation of theinvention makes it possible, by itself, in a combined refrigeration andheat pump operating mode, firstly to cool the refrigeration units andsecondly to heat the premises. Such a combined operating mode thus makesit possible to achieve serious energy savings for heating the premises.

Insofar as the temperature at the surface of the evaporator 18 isnegative in view of the expansion of the refrigerant fluid in it, thenafter a certain operating time, the evaporator 16 is covered in frostcoming from condensation and freezing of the water present in theoutside atmosphere. It is thus necessary to defrost the condenser 18regularly.

The invention proposes to perform this defrosting by using the heat fromthe compressed refrigerant fluid exiting from the compression units. Tothis end, the invention proposes to associate a condenser 25 with theevaporator 18. The condenser 25 fed with high-pressure refrigerant fluidby the main high-pressure circuit 2 by being connected thereto firstlydownstream from the compression units and secondly upstream from thetank 3 and from the evaporators of the main refrigeration units R_(P).In a preferred embodiment and as appears from FIGS. 2 and 3, theevaporator 18 comprises a tube circuit 30 for evaporating therefrigerant fluid, which circuit is formed by tube sheets 32 comprisingrectilinear main tubes as shown more particularly in FIG. 2. In the sameway, the condenser 25 comprises a tube circuit for condensing therefrigerant fluid, which circuit is made up of sheets 35 of tubes 36comprising rectilinear main tubes as shown in FIG. 2. The tube circuits30 and 35 are then connected together via thermally conductive fins 40that, in the example shown, extend substantially vertically. The thermallink by conduction that is provided by the fins 40 that are common tothe evaporation circuit 30 and to the condensation circuit 35 guaranteesthat the defrosting is highly effective. For further optimizing thequality of the heat exchanges and thus the effectiveness of thedefrosting in the embodiment shown, the tube sheets of the condensationcircuit 35 and of the evaporation circuit 30 are superposed on andinterleaved with one another. In addition, in the example shown, thefirst sheet of the heat exchanger 17 starting from the bottom is formedby tubes of the condensation circuit in such a manner as to form acondensation surface for condensing the water vapor present in the airwhile the exterior unit 15 is operating. Finally, it can be noted that,in a manner usual for the person skilled in the art, the heat exchanger17 is situated inside a covered frame 41 equipped at its top with atleast one and, in the example shown, with two fans 43 forcing air toflow through the exterior unit 15. In addition, in order to facilitateremoval of the liquid water resulting from the defrosting or from thecondensation, the rectilinear portions of the tubes and the fins may beinclined relative respectively to the horizontal and to the vertical byan angle a of a few degrees, e.g. in the range 3° to 5°. Thisinclination may be obtained by inclining the frame as a whole.

In the above-explained combined operating mode, it is also possible forprovision to be made, when the outside temperature is particularly low,for the compression of the refrigerant fluid coming from the evaporatorof the exterior heat exchanger to be staggered. To this end, theinstallation may have a bypass 55 connecting the outlet of the auxiliarycompression unit 21 upstream from the suction inlet of the maincompression unit 10 via a constant-pressure cock 56 controlled by theunit 12.

In addition, while the installation is operating in combined mode, thecondenser 25 is used regularly to defrost the evaporator 18. Thisregular operation can be achieved at predefined time intervalsindependently of the appearance of any frost on the evaporator 18 or,conversely, be a function of the needs when frost actually appears or afunction of the forecast appearance of frost.

To this end, the refrigeration installation 1 may implement means forassessing the frost. Such frost assessment means may be formed in anysuitable manner. For example, the frost assessment means may comprisemeans 45 for monitoring the load on the fans 43 that, when said loadexceeds a predetermined threshold, deduce therefrom that frost hasappeared. The frost that deposits on the tubes 30 and on the fins 40progressively obstructs the heat exchanger 17, making it more difficultfor air to flow therethrough so that the load on the fans 43 increases.

The frost detection means may also comprise a system that measures thehumidity of the air entering or leaving the exterior unit 15 so as todeduce therefrom whether any frost has appeared. The frost assessmentmeans may also comprise a system for measuring the humidity and thetemperature of the outside air so as to act, as a function of thosemeasurements, to forecast appearance of frost. Naturally, the frostassessment means are connected to the control unit 12 that, whenevernecessary, triggers a defrosting cycle.

During such a defrosting cycle, the unit 12 causes the condenser 25 tobe fed with hot high-pressure refrigerant fluid. This feeding isachieved via a branch of the main high-pressure circuit 2 that iscontrolled by a cock 46 controlled by the unit 12. The cock 46 thenmakes it possible to admit into the feed circuit of the condenser 25high-pressure refrigerant gas coming directly from the compression units10 and 21. In order to avoid a thermal shock that is too large at theheat exchanger 17, it is also possible to provide a bypass line 47making it possible to take high-pressure refrigerant fluid in the liquidstate from downstream from the tank 3. This bypass 47 is then controlledby a cock 48 controlled by the unit 12. Control of the cocks 46 and 48then makes it possible to mix the high-pressure gas coming from thecompression units with the high-pressure fluid coming from the tank 3 soas to modulate the temperature of the fluid in the condenser 25 in orderto bring the condenser and the fins progressively from a negativetemperature to a positive temperature that is higher but that is lessthan the temperature of the compressed refrigerant gas exiting from thecompression units. Thus, the unit 12 can maintain the temperature of therefrigerant fluid feeding the condenser 25 at values lying approximatelyin the range 40° C. to 60° C., while the maximum temperature at theoutlets of the compression units is about 80° C. Such a gradual rise intemperature prevents the heat exchanger 15 from being subjected to athermal shock that is too large.

When the defrosting is finished, the unit 12 can also cause the fans 41to operate in such a manner as to blow the outside air downwards tocontribute to drying the heat exchanger 17.

In the above-described combined refrigeration and heat pump operatingmode, the auxiliary compression unit 21 is used to extract heat from theoutside environment. However, in accordance with the invention, when itis no longer necessary to heat the premises, e.g. during the summerperiod, the auxiliary compression unit 21 can be used to reinforce themain compression unit for the purpose of compressing the refrigerant gascoming from the refrigeration units R_(P). To this end, therefrigeration installation includes a bypass circuit 50 connecting themain high-pressure circuit 4 to the auxiliary low-pressure circuit 20via a cock 51 controlled by the unit 12. Upstream from the junction withthe bypass 50, the auxiliary low-pressure circuit 20 also has a cock 52controlled by the unit 12. Thus, in an operating mode that can be saidto be a “purely refrigeration” mode, the unit 12 causes the cock 52 toclose and the cock 51 to open, and causes the auxiliary compression unit21 to operate as a function of needs. The power of said auxiliarycompression unit is then available for refrigeration, the condenser 25also being dimensioned to enable the heat extracted from therefrigeration units R_(P) to be removed to the outside. It can thus beunderstood that the power of the condenser 25 is then greater than orequal to the power of the evaporator 18. The thermal power of thecondensation tube circuit 25 may, for example, have a value lying in therange 1 times the absolute value of the thermal power of the evaporationtube circuit 18 to 5 times said absolute value. This power ratio can beobtained by making the heat exchanger 17 of the exterior unit 15 in sucha manner that the heat exchange surface area of the condensation tubecircuit 25 represents in the range 50% of the sum of the heat exchangesurface areas of the condensation and evaporation tube circuits 25 and18 to 80% of said sum.

In addition, in purely refrigeration mode, the cocks 45 and 47 areclosed, and the condenser 25 is fed via a constant-pressure cock 53controlled by the unit 12. In addition, in this purely refrigerationoperating mode, the evaporator 18 is not fed with refrigerant fluid andthe valve and the cock 19 are thus closed. The capacity of theinstallation of the invention to operate either in combined mode or inpurely refrigeration mode makes it possible to dimension the main andauxiliary compression units 10 and 21 with cumulative power justsufficient to guarantee optimum refrigeration in the summer period. Theterm “the summer period” is used to mean a period during which theaverage daytime temperature is greater than 18° C. Insofar as, in thewinter period, the power necessary for achieving suitable refrigerationis less than the power necessary in the summer period, the residualpower available at the auxiliary compression unit 21 may advantageouslybe used, in the winter period, for operation as a heat pump for heatingthe premises.

In the example described with reference to FIG. 1, the refrigerationunit only has main low-pressure and high-pressure refrigeration circuitsthat feed refrigeration units that operate within the same temperatureranges, either positive or negative. However, a refrigerationinstallation of the invention can be required to feed bothpositive-temperature refrigeration units and also negative-temperaturerefrigeration units. To this end, and as shown in FIG. 4, aninstallation of the invention may also have at least one secondaryrefrigeration unit R_(S) comprising at least one evaporator disposed ina piece of furniture or in a refrigerated room fed with refrigerantfluid by a main high-pressure circuit 2 downstream from the tank 3. Theevaporator of the secondary refrigeration unit R_(S) is connected to asecondary low-pressure circuit 60 that feeds a secondary compressionunit 61 sucking in the refrigerant fluid from the secondary low-pressurecircuit 60 so as to deliver it into the main high-pressure circuit 2.The secondary compression unit 61 then comprises at least one and, inthe example, two compressors 62 that are controlled by the control unit12. Operation of the refrigeration installation of the inventionincluding such a secondary low-pressure circuit 60 and a secondarycompression unit 61 is then substantially analogous to the operationdescribed above as regards the combined and the purely refrigerationoperating modes.

It should be noted that, in the example shown in FIG. 4, therefrigeration installation includes a liquid heat exchanger 63 connectedfirstly to the high-pressure circuit 2 in parallel with the heatexchangers 5 and secondly to a circuit 64 through which a heat transferliquid flows. The liquid heat exchanger 63 that is fed under the controlof a valve 65 controlled by the control unit UC then makes it possibleto heat the liquid in the circuit 64.

It should also be noted that the condenser 25 is placed on the mainhigh-pressure circuit 2 in parallel with the heat exchangers 6 and/or63. Thus, depending on the operating stages, it is possible to empty theliquid phase of the refrigerant fluid from the non-used circuit portionsvia suction lines 67 and 68 controlled by valves 68 and 69 that arecontrolled by the unit 12. The suction lines 67 and 68 are alsoconnected, via an expansion member 70, to the main low-pressure circuit4 immediately upstream from the main compression unit 10. Thisconfiguration makes it possible to reduce the quantity of refrigerantfluid used by the installation compared with installations in which nopartial emptying of the liquid phase is possible.

Naturally, various other modifications may be made to the inventionwithin the ambit defined by the claims.

1-14. (canceled)
 15. A refrigeration installation having refrigerantfluid and comprising at least: high-pressure and a low-pressurecircuits; a refrigeration unit comprising at least one evaporatordisposed in a piece of furniture or in a walk-in cooler, and connectedto the high-pressure and low-pressure circuits; an air-conditioning unitcomprising at least one heat exchanger that is disposed inside a room ofpremises, and that further comprises at least one condenser connected tothe high-pressure and low-pressure circuits; an exterior unit comprisingat least one air heat exchanger that is disposed outside and thatcomprises a condensation tube circuit connected to the high-pressure andlow-pressure circuits; a main compression unit connected to thehigh-pressure and low-pressure circuits; an auxiliary compression unitconnected to the high-pressure and low-pressure circuits; and a controlunit that controls operation of the refrigeration installation; whereinthe air heat exchanger of the exterior unit further comprises: anevaporation tube circuit adapted to be fed with low-pressure refrigerantfluid only and connected to the high-pressure and low-pressure circuits;and thermally conductive fins interconnecting the evaporation tubecircuit and the condensation tube circuit by being secured to theevaporation and condensation tube circuits; the condensation tubecircuit being adapted to be fed with high-pressure refrigerant fluidonly and being dimensioned so as to dissipate all of the heat resultingfrom keeping each refrigeration unit at temperature settings when asummer temperature prevails outside; wherein the control unit is adaptedto place the installation: either in a purely refrigeration operatingmode, in which the power of all of the compression units is availablefor extracting heat from each refrigeration unit only; or in a combinedrefrigeration and heat pump operating mode, in which the power of theauxiliary compression unit is available for extracting heat from theexterior unit, and the power of each other compression unit is availablefor extracting heat from each refrigeration unit; and wherein thecompression units are dimensioned so that their cumulative power issufficient for maintaining each refrigeration unit at temperaturesettings when a summer temperature prevails outside and when theinstallation is in purely refrigeration mode.
 16. A refrigerationinstallation according to claim 15, wherein the control unit is adaptedto go from the combined operating mode to the purely refrigerationoperating mode and vice versa as a function of the refrigeration needs.17. A refrigeration installation according to claim 15, wherein thecontrol unit is adapted so that, in combined operating mode, it causesthe condensation circuit of the exterior unit to be fed in order todefrost the exterior unit.
 18. A refrigeration installation according toclaim 17, wherein the installation further comprises frost assessmentmeans for assessing the frost on the heat exchanger, and wherein thecontrol unit is adapted to cause the condensation circuit to be fedwhenever the frost on the heat exchanger exceeds a certain threshold.19. A refrigeration installation according to claim 15, wherein theinstallation further comprises: a secondary low-pressure circuit forrefrigerant fluid; a secondary refrigeration unit comprising at leastone evaporator that is disposed in a piece of furniture or in a walk-incooler, that is fed with refrigerant fluid by the high-pressure circuit,and that is connected to the secondary low-pressure circuit; and asecondary compression unit that sucks in refrigerant fluid from thesecondary low-pressure circuit (60) and that delivers compressedrefrigerant fluid into the high-pressure circuit; and wherein thecontrol unit is adapted to cause the secondary compression unit tooperate.
 20. A refrigeration installation according to claim 15, whereinthe absolute value of the thermal power of the condensation tube circuitof the air heat exchanger is greater than or equal to the absolute valueof the thermal power of the evaporation tube circuit of the air heatexchanger.
 21. A refrigeration installation according to claim 15,wherein the thermal power of the condensation tube circuit of the airheat exchanger has a value lying in the range 1 times the absolute valueof the thermal power of the evaporation tube circuit of the air heatexchanger to 5 times said absolute value.
 22. A refrigerationinstallation according to claim 15, wherein the heat exchange surfacearea of the condensation tube circuit of the air heat exchangerrepresents in the range 50% of the sum of the heat exchange surfaceareas of the condensation and evaporation tube circuits to 80% of saidsum.
 23. An exterior air heat exchanger for a refrigeration installationaccording to any one of claims 15, said exchanger comprising: acondensation tube circuit adapted to be fed with high-pressurerefrigerant fluid only; an evaporation tube circuit adapted to be fedwith low-pressure refrigerant fluid only; and thermally conductive finsinterconnecting the evaporation tube circuit and the condensation tubecircuit by being secured to the evaporation and condensation tubecircuits; the absolute value of the thermal power of the condensationtube circuit being greater than or equal to the absolute value of thethermal power of the evaporation tube circuit.
 24. An exterior air heatexchanger according to claim 23, wherein the thermal power of thecondensation tube circuit has a value lying in the range 1 times theabsolute value of the thermal power of the evaporation tube circuit to 5times said absolute value.
 25. An exterior air heat exchanger accordingto claim 23, wherein the heat exchange surface area of the condensationtube circuit represents in the range 50% of the sum of the heat exchangesurface areas of the condensation and evaporation tube circuits to 80%of said sum.
 26. A heat exchanger according to claims 23, wherein thecondensation circuit and the evaporation circuit comprise loops or tubesheets and in that certain loops or sheets of the evaporation circuitare superposed on and interleaved between the loops or sheets of thecondensation circuit.
 27. A heat exchanger according to claims 23,wherein the fins extend substantially vertically.
 28. A heat exchangeraccording to claim 23, wherein the condensation circuit comprises atleast one tube sheet that forms the first tube sheet starting from thebottom of the heat exchanger.